The present invention relates to an exhaust mechanism of a pneumatic nailing machine for discharging the exhaust air after a nail has been driven by the pneumatic nailing machine.
By a pneumatic nailing machine in which compressed air is used, a nail is driven when a driver is activated together with a striking piston incorporated into a striking cylinder into which compressed air is supplied. After the completion of driving a nail, the compressed air is directly discharged outside the nailing machine from an upper end of the striking cylinder.
Recently, it is allowed to use compressed air of high pressure for industrial use. Therefore, when compressed air of high pressure is used for a pneumatic nailing machine, it is possible to develop a compact, handy nailing machine, the capacity of which is the same as the capacity of a conventional nailing machine.
Although it is possible to obtain a large capacity when compressed air of high pressure is used, the level of exhaust sound is raised. In order to reduce the level of exhaust sound, it is considered to adopt a mechanism in which compressed air is discharged from the striking cylinder via an exhaust chamber.
However, even if exhaust air is discharged via the exhaust chamber, when it is directly discharged from the exhaust chamber, the wind pressure generated by the exhaust air is increased. Therefore, a cloud of dust is made, so that the worker feels uneasy and uncomfortable, and the nailing operation is affected. For this reason, it is desired to develop a mechanism capable of reducing the wind pressure caused by exhaust air. However, when a new mechanism is added to the nailing machine, the size of the overall nailing machine is increased.
Furthermore, although it is possible to obtain a nailing machine of high capacity by using compressed air of high pressure, the level of exhaust sound is raised. In order to reduce the level of exhaust air sound, several methods are provided, for example, an exhaust hole may be throttled, or a filter is arranged in the exhaust air passage. However, when these methods are adopted, the exhaust of air is delayed. Therefore, the striking piston returning performance is deteriorated when the striking piston returns after the completion of driving a nail. Further, the effect of sound reduction is not so high.
FIG. 18 shows a conventional pneumatic nailing machine shown in which a short cylindrical head valve is arranged on the upper outside of a striking cylinder 32. When a head valve 30 is opened, compressed air in an air chamber 31 flows into a clearance between the head valve 30 and the striking cylinder 32. Then, compressed air is suddenly supplied into the striking cylinder 32 from an upper end opening of the striking cylinder 32 as shown by the arrow in the drawing. By the pressure of the compressed air, the driver 34 is actuated together with a striking piston 33 arranged in the striking cylinder 32, so that a nail can be driven.
When the head valve 30 is opened and the compressed air of high pressure in the air chamber 31 flows into the clearance between the head valve 30 and the striking cylinder 32 as described above, the compressed air is suddenly expanded. Due to the above adiabatic expansion, the temperature of the compressed air is lowered. Therefore, the moisture contained in the compressed air is frozen on an upper outer circumferential surface "a" of the striking cylinder 31. Due to the foregoing, the head valve to control the supply and discharge of the compressed air is not properly operated, because the head valve can not be sealed properly so that the compressed air leaks out. Therefore, the following problems may be encountered. A striking force is not strong enough to drive a nail, or a lost nailing motion is conducted by the nailing machine.